Multiple heat range spark plug

ABSTRACT

A spark plug that is provided with a heat shunt on the plug insulator nose arranged such that the characteristics of a &#39;&#39;&#39;&#39;hot&#39;&#39;&#39;&#39; plug are produced at lower operating temperatures and of a &#39;&#39;&#39;&#39;cold&#39;&#39;&#39;&#39; plug at higher operating temperatures. The heat shunt is a thermally conductive sleeve surrounding the insulator nose in the bore of the spark plug shell. A thermal gap between the heat shunt and the plug insulator nose prevents heat transfer through the shunt at lower operating temperatures - there is thus a relatively long heat path into the engine cooling system and the firing end of the plug stays relatively hot to prevent fouling. At higher operating temperatures, the heat shunt expands thermally to bridge the gap to thereby shorten the heat path into the cooling system so that the relatively rapid heat conduction &#39;&#39;&#39;&#39;cools&#39;&#39;&#39;&#39; the firing end of the plug to prevent its overheating under high speeds and loads. The heat shunt can be used with air gap, surface gap, and other types of spark plugs.

United States Patent [1 1 Strumbos July 3,1973

[ MULTIPLE HEAT RANGE SPARK PLUG [76] inventor: William P. Strumbos, 85 Middleville Road, Northport, NY. 11768 [22] Filed: Oct. 12, 1971 [21] Appl. No.: 188,176

Primary ExaminerAlfred L. Brody [5 7] ABSTRACT A spark plug that is provided with a heat shunt on the plug insulator nose arranged such that the characteristics of a hot" plug are produced at lower operating temperatures and of a cold" plug at higher operating temperatures. The heat shunt is a thermally conductive sleeve surrounding the insulator nose in the bore of the spark plug shell. A thermal gap between the heat shunt and the plug insulator nose prevents heat transfer through the shunt at lower operating temperatures there is thus a relatively long heat path into the engine cooling system and the firing end of the plug stays relatively hot to prevent fouling. At higher operating temperatures, the heat shunt expands thermally to bridge the gap to thereby shorten the heat path into the cooling system so that the relatively rapid heat conduction cools the firing end of the plug to prevent its overheating under high speeds and loads. The heat shunt can be used with air gap, surface gap, and other types of spark plugs.

5 Claims, 10 Drawing Figures SHUNT EXPANDED- "PLUG" COLD RANGE 2 Sheets-Sheet 1 Patented July 3, 1973 SHUNT CONTRACTED- 2 "PLUG" HOT RANGE FIG.

(A EN MULTIPLE HEAT RANGE SPARK PLUG CROSS-REFERENCES TO RELATED APPLICATIONS The present application is for an improvement of the spark plug of my copending application, Ser. No. 18,615, filed Mar. 11, 1970, now US. Pat. No. 3,612,931.

BACKGROUND OF THE INVENTION This invention relates to spark plugs for internal combustion engines and, more particularly, to a spark plug which is provided with means to vary the heat range of the plug automatically.

Spark plugs, particularly those in high-speed, highcompression engines, are subjected to an extreme range of pressure and thermal conditions. Plug temperatures range from about 400 F at low engine speeds and light loads, to as high as 1600 F under full throttle, full load. Below about 840 F, carbon and other products of combustion begin to form on the plug insulator nose. If not removed, those deposits build up until current shorts through the deposits instead of sparking across the electrodes. At normal speeds, enough heat is usually generated to burn those deposits away as quickly as they are formed. However, when high speeds or heavy loads raise the plug temperatures above 1,100 to 1,300 F, the deposits, particularly those resulting from the additives in currently available fuels and lubricants, are melted to form a glaze coating on the plug insulator nose. When hot, this glaze is highly conductive and the plug is shorted out. This causes misfiring with consequent fuel and power losses. Should plug temperatures become excessive, the plug points themselves become hot enough to ignite the fuel-air mixture in the cylinder. This causes auto-ignition and, if continued, can lead to'the destruction of the plug and serious engine damage. Overheated electrodes also cause a condition commonly met in two-stroke engines: the bridging of the electrodes due to the build-up of conducting deposits formed by combustion particles which have melted upon their striking the overheated electrodes. ln plug temperatures ranging above l,600 F, chemical corrosion and spark erosion cause plug failure within a very short time.

It will be seen then, if a hot-type plug is subjected to high compression pressures, temperatures, and loads, electrode burning and auto-ignition will result because of the plugs slow rate of heat transfer. A cold plug, because it will not reach full operating temperature, will not tolerate low-speed, light-load operation for any length of time without becoming fouled with currentconducting deposits. Because a cold plug under such conditions will not reach a temperature required to burn off fouling, carbon formation as well as additive particles from the fuel and oil will condense on the comparatively cool surfaces of the insulator to foul the plug and cause it to misfire.

Spark plugs are customarily supplied in various heat ranges to handle the requirements of individual engines and operating conditions. Heat range refers to the ability of the plug to conduct the heat of combustion away from the electrodes or firing end. As shown in FIG. 1, a hot-type plug 2 will have a long insulator nose 3. Because of the length of the heat path (as indicated by the arrows 4), heat thus will be transferred comparatively slowly from the plug firing end to the engine cooling system 5. A cold-type plug 6 (FIG. 2), on the other hand, has a comparatively short insulator nose 7 and heat is transferred rapidly (as indicated by arrows 8) into the engines cooling system.

SUMMARY OF THE INVENTION In my multiple heat range spark plug as set forth in US. Pat. No. 3,612,931, referenced above, the heat range is varied automatically as required in response to the engine cylinder operating temperatures by a heat shunt bonded on the plug insulator nose. By bonding the heat shunt directly on the insulator, good heat transfer from the insulator to the shunt is assured; however, the bonding step during the manufacture of the plug adds a cost penalty that is reflected undesirably in the selling price of the device. I have found that it is possible to take advantage of the thermal expansion properties of the heat shunt to provide a mechanical action that will force the shunt as it is heated into a good thermal contact with the insulator. Thus, good heat transfer from the insulator to the heat shunt is assured without the requirement which adds to the cost of the device of having the shunt bonded to the insulator.

DESCRIPTION OF THE DRAWINGS For the purpose of illustrating the invention, there is shown in the drawings the forms which are presently preferred, it being understood, however, that this invention is not necessarily limited to the precise arrangements and instrumentalities here shown.

FIG. 1 is a side elevation in partial longitudinal section of a prior art spark plug of the hot type in its operating environment in an engine cylinder head;

FIG. 2 is a similar view of a prior art spark plug of the cold type;

FIG. 3 is a side elevation in partial longitudinal section of a spark plug embodying the heat shunting means of the invention;

FIG. 4 is a side elevation in partial section of the spark plug of FIG. 3 in place in the cylinder head of an engine and showing the heat path in the hot range of the invention;

FIG. 5 is a similar view of the spark plug of FIG. 3 showing the heat path in the cold range of the invention;

FIG. 6 is an enlarged view in partial section of the lower end of the plug of FIG. 3 showing details of construction;

FIG. 7 is a perspective view of the heat shunt of the invention;

FIG. 8 is a view in section of the embodiment of FIG. 3 taken along line 8-8 of FIG. 6;

FIG. 9 is a partial sectional view of the lower end of a plug showing a further embodiment of the invention; and 1 FIG. 10 is a fragmentary detail view enlarged to show details of construction of the embodiment of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 3 of the drawings, there is shown a spark plug 10 comprising an insulator ll positioned within a metal shell 12 in a gas-tight relationship therewith. The insulator 11 is formed of alumina or other suitable material in the conventional manner with an upper shoulder 13 and a lower shoulder 14. A sealing gasket is positioned on upper shoulder 13 and a sealing gasket 16 is provided between the lower shoulder l4 and an annular ramped portion or ledge 17 formed in the bore of the shell 12. The insulator 11 has a body portion 18 and a tapered nose portion 19 and is provided with a centerbore within which is secured a conventional center electrode assembly having a tip portion 20. Tip 20 of the center electrode assembly protrudes from the lower end of the insulator 11 and constitutes a firing tip which forms a spark gap in a fashion well known in the art with a ground electrode 21 which is suitably attached as by welding to the lower end of the shell 12. The shell has a shoulder 22 below which is a threaded portion 23 formed to engage in a well-known manner in a threaded bore 24 in the cylinder head 25 of an engine 26 (See FIG. 4). A gasket (not shown) can be provided if required as a sealing means between shoulder 22 and cylinder head 25. The cylinder head normally is provided with cooling means, typically passages 27 through which is circulated a coolant such as fluid 28 for cooling the engine. It will be appreciated that details of the engine are given merely for purposes of exposition only and it forms no part of the invention.

It will also be appreciated that the spark plug as described to this point is substantially a conventional spark plug fabricated with well known materials using suitable known techniques. The instant invention resides in the provision of heat shunting means on the nose portion 19 of the plug insulator 11. As explained in the aforementioned US. Pat. No. 3,612,931, the design of the heat shunt is susceptible to many variations with regard to construction, size, and arrangement, but in the preferred embodiment herein the heat shunt 29 comprises a sleeve 30, suitably of metal, fitted in the bore 31 in the lower portion of shell 11 and secured therein as by swaging 32 the lower rim 33 of the shell (FIG. 6). Shunt 29 has a bore 34 which is provided with a taper matching the tapered nose portion 19 of the insulator. Between the outer peripheral face 35 of the insulator and the inside wall surface 36 of the bore 34 of the shunt when the plug 10 is below a certain design temperature is an annular gap 37. Shunt 29 has a longitudinal split 38 extending completely through the wall 39 of the shunt and its lower end 40 is bevelled 41 (FIG. 7). A fouling shield 42 fabricated from mica, ceramic, or other suitable material is bonded by appropriate means such as a ceramic cement 43 to the center electrode 20 and the lower inside edge 44 of the shell bore such that the heat shunt is shielded effectively from the combustion products in its operating environment.

With the exception of the spark plug thermal control provided by the heat shunt, the plug performs in a conventional manner to ignite the fuel/air mixture in the engine cylinder. With respect to the heat shunt for varying the heat range of the plug automatically, in operation, below some specific temperature, known as the design temperature, the heat shunt gap 37 provides a barrier to heat flow such that heat from the firing end 20 of the plug is required to pass up the insulator nose l9 and, by means of gasket 16, through the shell 12 before it passes, as indicated by arrows 44, into the cooling system of the engine (FIG. 4). Because of the relatively long heat path, heat is transferred slowly from the firing end such that the plug runs at a temperature which is high enough to be free of deposit fouling problems even during prolonged periods of idle or lowspeed operation. This may be considered to be the hot" range of the device.

When the operating temperature rises above the design point, the heat shunt 29 will expand thermally in all directions. Outward expansion of the outer wall of the shunt is restricted by the bore 31 of the shell and the shunt growth will be forced in the direction indicated by arrows 45 and 46 as shown in FIG. 8 such that edge 47 of longitudinal split 38 is forced under edge 48 to thereby contract the bore 34 of the shunt as depicted by arrows 49 into thermal contact with the peripheral face 35 of the insulator nose 19, closing shunt gap 37. It will be appreciated that there will also be a longitudinal growth of the heat shunt as indicated by directional arrow 50 in FIG. 6 that also serves to close the gap. With the closing of the thermal gap, heat is transferred rapidly away from the firing end 20 of the plug, passing by means of the shunt 29 directly into the plug shell 12 and thence into the cooling system of the engine as indicated by directional arrows 45 (FIG. 5). Because of the relatively short heat path, heat is transferred rapidly from the firing end such that the plug temperatures remain relatively low to thereby avoid pre-ignition and thermal erosion problems. This may be considered to be the cold range of the spark plug.

Good design practice dictates that the heat shunt be fabricated from a material (or materials, if a composite or a bimetallic shunt construction is used) of high thermal conductivity having good thermal contact with the shell and insulator when the plug is operating above its design temperature. The width of the gap between the shunt and the insulator is determined by the coefficient of thermal expansion of the heat shunt (compensation being made, of course, for the thermal growth of the insulator and of the shell itself) and is calculated such that the expansion of the shunt will close the gap and establish good thermal contact with the insulator and shell at some predetermined plug temperature. To avoid plug fouling that occurs at plug temperatures below about 900 F, the heat shunt should be designed to become effective at about that temperature, preferably somewhere in the range between 900 and l,l00 F. When the heat shunt gap closes, heat will be conducted rapidly away from the firing end of the plug in a manner analogous to a cold-type plug to allow high cylinder temperatures to be accommodated without damage or loss of performance. The temperature at which the thermal expansion of the heat shunt has caused it to expand into good thermal transfer contact with the insulator and shell is the design temperature: this temperature will preferably be in the 900 l,l00 F range, but the design temperature can be changed to suit the requirements.

Although the foregoing description is of a singleelectrode plug, the invention is not to be construed as being limited to such type and the scope of the inven tion embraces the other types such as, for example, the multiple-electrode and surface-gap type spark plugs. Thus, the heat shunt of this invention can be incorporated in a surface-gap spark plug 10a of the embodiment of FIG. 9. Except for details of the firing end of the plug, this embodiment is essentially similar to the single-electrode plug of FIG. 3 and thus details of construction of the shell 12, insulator 11, and heat shunt 29 are identical. The center electrode of the firing end 20a of the plug is shortened and the ground electrode 21a is typically of an annular metal type fixed in the lower inside edge 44 of the plug shell 12 as by welding 51 as perhaps best shown in the detail view of FIG. 10. As is usual in this type of plug, an annular spark gap 52 is formed between the center electrode and the ground electrode. As is also known, a electrically semiconducting ceramic material 53 can be provided in the annulus between the center electrode and the ground electrode. However, if desired, instead of employing a semi-conducting ceramic, material 53 can be a ceramic cement for sealing the bore of the spark plug shell to thereby isolate the heat shunt from the combustion products of its operating environment.

In operation, the spark plug 100 embodied in FIG. 9 operates as a typical surface gap plug and the operation of the heat shunt 29 to control the heat range of the device is identical to the operation of the heat shunt 29 of the embodiment of FIG. 1. It is not believed, therefore, that it would serve any useful purpose to repeat the description of the operation of the device.

Thus, although shown and described in what are believed to be the most practical and preferred embodiments, it is apparent that departures therefrom will suggest themselves to those skilled in the art and may be made without departing from the spirit and scope of the invention. I, therefore, do not wish to restrict myself to the particular details illustrated and described, but desire to avail myself of all modifications that may fall within the scope of the appended claims.

Having thus described my invention, what I claim is:

1. In a spark plug having a shell with a bore, an annular ledge in said shell bore intermediate the ends thereof, sealing means comprising at least a sealing gasket on said ledge, an insulator subassembly positioned on said gasket in a gas-tight relationship in said bore, said insulator subassembly having an insulator with a center electrode positioned therein and a firing end portion in a spaced apart relationship with the surrounding wall surface of said bore of said shell, ground electrode means on said shell positioned in an operative relationship with said center electrode, the improvement for varying automatically the heat range of said spark plug comprising a thermally conductive heat shunt positioned spaced from and out of contact with said gasket in the spaced apart region between said insulator and said bore of said shell, said heat shunt in one temperature range being out of heat conducting contact with said insulator such that heat is not conducted therethrough from said insulator to said shell, said shunt having integrally bevelled camming means actuated by its thermal expansion characteristics whereby in a second temperature range it is moved into heat conducting contact with the insulator and shell so as to provide a relatively short heat path from said insulator into said shell such that the temperature of the spark plug firing end portion is thereby modified.

2. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face and wherein said inner face is tapered and the mating surface of the insulator outer surface in operative association with said heat shunt has a matching taper.

3. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve in thermal contact with the spark plug shell in the first and second temperature ranges of the shunt.

4. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face, said shunt having a first integral bevelled portion free to be displaced relative to a second integral bevelled portion thereof, said outer face being restricted in its radial travel during thermal growth by the bore of the shell, and wherein in the second temperature range the restriction presented by said shell bore to the thermal expansion of said shunt causes said first bevelled portion to be displaced relative to said second portion to thereby move said inner face into thermal contact with the insulator such that heat therefrom is conducted through said shunt into said shell.

5. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face, said outer face being restricted in its radial travel during thermal growth by the bore of the shell, and wherein the means for actuating the shunt is a longitudinal slit cut tangentially through the wall of said sleeve, the sides of said slit forming first and second ramp portions such that radial thermal growth of said sleeve is forced by the restriction presented by said shell bore into a circumferential expansion in which said first ramp portion is moved upon said second ramp portion so as to constrict the bore of said sleeve whereby in the second temperature range said inner face of said sleeve is brought into thermal contact with said insulator such that heat therefrom is conducted through said shunt into said shell. 

1. In a spark plug having a shell with a bore, an annular ledge in said shell bore intermediate the ends thereof, sealing means comprising at least a sealing gasket on said ledge, an insulator subassembly positioned on said gasket in a gas-tight relationship in said bore, said insulator subassembly having an insulator with a center electrode positioned therein and a firing end portion in a spaced apart relationship with the surrounding wall surface of said bore of said shell, ground electrode means on said shell positioned in an operative relationship with said center electrode, the improvement for varying automatically the heat range of said spark plug comprising a thermally conductive heat shunt positioned spaced from and out of contact with said gasket in the spaced apart region between said insulator and said bore of said shell, said heat shunt in one temperature range being out of heat conducting contact with said insulator such that heat is not conducted therethrough from said insulator to said shell, said shunt having integrally bevelled camming means actuated by its thermal expansion characteristics whereby in a second temperature range it is moved into heat conducting contact with the insulator and shell so as to provide a relatively short heat path from said insulator into said shell such that the temperature of the spark plug firing end portion is thereby modified.
 2. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face and wherein said inner face is tapered and the mating surface of the insulator outer surface in operative association with said heat shunt has a matching taper.
 3. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve in thermal contact with the spark plug shell in the first and second temperature ranges of the shunt.
 4. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face, said shunt having a first integral bevelled portion free to be displaced relative to a second integral bevelled portion thereof, said outer face being restricted in its radial travel during thermal growth by the bore of the shell, and wherein in the second temperature range the restriction presented by said shell bore to the thermal expansion of said shunt causes said first bevelled portion to be displaced relative to said second portion to thereby move said inner face into thermal contact with the insulator such that heat therefrom is conducted through said shunt into said shell.
 5. A spark plug as defined in claim 1 wherein the heat shunt is a thermally conductive sleeve having an inner and an outer face, said outer face being restricted in its radial travel during thermal growth by the bore of the shell, and wherein the means for actuating the shunt is a longitudinal slit cut tangentially through the wall of said sleeve, the sides of said slit forming first and second ramp portions such that radial thermal growth of said sleeve is forced by the restriction presented by said shell bore into a circumferential expansion in which said first ramp portion is moved upon said second ramp portion so as to constrict the bore of said sleeve whereby in the second temperature range said inner face of said sleeve is brought into theRmal contact with said insulator such that heat therefrom is conducted through said shunt into said shell. 